This research is intended to determine how specialized cell types become directed into specific pathways of cellular differentiation, using the rat salivary glands as an experimental model. It focuses on the transient secretory proteins of the perinatal submandibular gland, and on their transformation into mature acinar cells. The work will examine cells in the small ducts of the adult gland, since these alone continue to express the unique protein products of the perinatal cells. Antibodies to the perinatal proteins will be used to identify by immunocytochemistry the several cellular phenotypes recognizable in these ducts, and determining their capacity to participate in normal and trauma-induced cellular replacement, using 3H-thymidine incorporation and following the changes in the cells as they differentiate. Studies will be initiated to determine whether a similar perinatal system exists in humans, and if this might be relevant to the potential for cellular replacement therapies in human exocrine glands. This work will also approach the question of the function and regulatory control of an unusual membrane-associated protein (Protein D) found in the two cell types of the perinatal gland and in the serous demilune cells of the sublingual gland. The experiments will examine the hypotheses that Protein D is attached to the membrane by a glycophospholipid anchor and functions to package other proteins for secretion. Ultracentrifugation will be used to isolate secretion granules and biochemical methods will determine the nature of the membrane association. The kinetics of processing and secretion will be studied by immunogold electron microscope analysis, after rapid freezing and freeze- substitution. An approach to the regulation of the perinatal genes will be continued through a gene cloning analysis, by screening a cDNA expression library for Protein D clones and determining its sequence.